1. Field of the Invention
This disclosure relates generally to graphics processing, and in particular to a processing unit, method, and medium of texture decompression.
2. Description of the Related Art
Computer graphics processing systems process large amounts of data, typically with a graphics processing unit (GPU) performing a large percentage of the processing. A GPU is a complex integrated circuit that is configured to perform, inter alia, graphics-processing tasks. For example, a GPU may execute graphics-processing tasks required by an end-user application, such as a video-game application. The GPU may be a discrete device or may be included in the same device as another processor, such as a central processing unit (CPU).
A GPU produces the pixels that make up an image from a higher level description of its components in a process known as rendering. GPU's typically utilize a concept of continuous rendering by the use of computing elements to process pixel, texture, and geometric data. The computing elements may execute the functions of rasterizers, setup engines, color blenders, hidden surface removal, and texture mapping. These computing elements are often referred to as shaders, shader processors, shader arrays, shader pipes, shader pipe arrays, shader pipelines, or a shader engine, “shader” being a term in computer graphics referring to a set of software instructions or a program used by a graphics resource primarily to perform rendering effects. “Shader” may also refer to an actual hardware component or processor used to execute software instructions. A shader processor or program may read and render data and perform any type of processing of the data. GPU's equipped with a unified shader also simultaneously support many types of shader processing, from pixel, vertex, primitive, and generalized compute processing.
Much of the processing involved in generating complex graphics scenes involves texture data. Textures may be any of various types of data, such as color, transparency, lookup tables, or other data. In some embodiments, textures may be digitized images to be drawn onto geometric shapes to add visual detail. A large amount of detail, through the use of textures, may be mapped to the surface of a graphical model as the model is rendered to create a destination image. The purpose of texture mapping is to provide a realistic appearance on the surface of objects. Textures may specify many properties, including colors, surface properties like specular reflection or fine surface details in the form of normal or bump maps. A texture could also be image data, color or transparency data, roughness/smoothness data, reflectivity data, etc. A ‘texel’ is a texture element in the same way a ‘pixel’ is a picture element. The terms ‘texel’ and ‘pixel’ may be used interchangeably within this specification.
In 3D computer graphics, surface detail on objects is commonly added through the use of textures. For example, a 2D bitmap image of a brick wall may be applied, using texture mapping, to a set of polygons representing a 3D model of a building to give the 3D rendering of that object the appearance that it is made of bricks. Providing realistic computer graphics typically requires many high-quality, detailed textures. The use of textures can consume large amounts of storage space and bandwidth, and consequently textures may be compressed to reduce storage space and bandwidth utilization.
Texture compression has thus become a widely accepted feature of graphics hardware in general and 3D graphics hardware in particular. The goal of texture compression is to reduce storage and bandwidth costs on the graphics system while retaining as much of the quality of the original texture as possible. The compression and decompression methods described herein may be used to compress various types of texture information including image data, picture data, transparency information, smoothness or roughness data, or any other similarly structured data. As such, the term texture is used broadly herein to refer to the data being compressed or decompressed as part of a GPU.
Fixed-rate compression schemes have traditionally been used to compress textures and may generally suffer from several shortcomings as compared to variable-rate schemes. Unlike fixed-rate compression, variable-rate compression is more flexible and may allow for adjustments to quality as desired. For example, variable-rate compression may be set to achieve lossless compression. In some cases, the use of variable-rate compression schemes may provide better compression than traditional fixed-rate compression schemes. A variable-rate compression scheme, such as Joint Photographic Experts Group (JPEG), is typically not used for texture compression when on-the-fly decompression is desired due to the high complexity and implementation cost. Therefore, there is a need in the art for methods and mechanisms to enable low-cost on-the-fly decompression of variable-rate compressed textures.
In view of the above, improved processing units, methods, and mediums for performing real time decompression of compressed textures are desired.